A digital oscilloscope may include a roll mode. In the roll mode, waveform data is added to the right hand edge of the screen as it becomes available. Existing data is shifted to the left as this new data is drawn. As a result, the user is able to capture all of the activity associated with a signal with a reduced possibility of missing information.
The data displayed in the roll mode moves across the screen at a rate in time related to the acquisition rate. Specifically, the refresh rate of the display screen (typically 30 Hz) controls when the waveform will be moved across the screen, and the acquisition rate determines how far across the screen the waveform will be moved. However, because of the large amount of data displayed on a screen and the limited resolution of a screen, events occurring over a short period of time may not be visible. To examine a waveform in greater detail, a user may wish to zoom in on such small events.
However, because of the large amounts of data involved and the relatively slow speed of converting the data into a displayable image, roll mode has typically been implemented without the benefit of a zoom feature. Even if a zoom feature is implemented, the zoom display operates in roll mode with the same number of samples appearing in the zoom display as the main display. Since the zoom display displays the waveform with a smaller time base, and the data is appearing at the same rate in both displays, the waveform appears to be moving through the zoom display at a faster rate. In fact, as the magnification of the zoom display is increased, the rate at which the data appears to move through the zoom display is increased. Thus, an event occurring over a short time period would only be visible in the zoom display for a short amount of time.
Accordingly, there remains a need for an improved apparatus and method for displaying digitized waveforms.